In the United States, directory numbers (DNs) are administered according to the North American Numbering Plan (NANP). The area served by the NANP is divided into smaller Numbering Plan Areas (NPAs), each identified by a three-digit NPA code, commonly called an area code. When the geographic or non-geographic area associated with a particular NPA substantially exhausts a large proportion of its DNs, it becomes necessary to create a new NPA that is assigned to new subscribers in the area (NPA overlay) or to a certain segment of the existing subscribers (NPA split) to increase the DNs that can be assigned in the area. Typically, a new NPA code is required when the 800 or more of the central office codes (NXXs) in the NPA are assigned or otherwise unavailable.
More specifically, an NPA is generally split by creating at least one new NPA, assigning the new NPA to a portion of the subscribers in the overburdened area, and retaining the old NPA for the remainder of the subscribers in the area. Thus, an NPA split typically changes the mobile directory numbers (MDNs) of at least some of the wireless devices in the affected area.
To implement an NPA split in the context of a typical GSM (Global System for Mobile communications) wireless network, an update is pushed to the Home Location Register (HLR) and to other affiliated network elements that are associated with the affected wireless devices. The HLR maintains a service subscription record for each wireless device, the record including: a non-dialable, permanent identifier unique to the wireless device, such as an IMSI; the dialable and portable MDN, which is stored in the format referred to as an MSISDN (Mobile Station International Integrated Service Digital Network Number), according to the E164 standard defined by the ITU-T (International Telecommunications Union—Telecommunications Standardization Sector); and various other subscriber data. The term “update” is commonly used to refer to the process by which a network element or device is accessed to add, delete, reorganize, or revise subscriber data and/or software. In the context of an update pursuant to an NPA split, HLR records are updated at least in part by modifying the MSISDN associated with each affected device to replace the old NPA with the new NPA. Another update must be provisioned, preferably over-the-air (OTA), to each affected device to change the locally maintained MSISDN, which may be stored in a memory module such as a Subscriber Identity Module (SIM) card.
For an HLR update to be successful, it must be synchronized with updates of records in various other network elements that contain corresponding subscriber data. For example, the MDN associated with a subscriber or wireless device is typically maintained in the billing system, voicemail system, the data services database, and other affiliated network elements. In order to deliver the services included in the subscription and to correctly bill the subscriber, the subscriber data maintained by all of these affiliated elements must correlate with the service subscription record in the HLR. Therefore, updates are typically staged via a central provisioning system, which coordinates updates of the HLR and the affiliated networks.
Carriers are required to provide a period of permissive dialing (PD), as defined by the NANP, which allows callers to dial either the old MDN including the old NPA or the new MDN including the new NPA, and still transparently reach the intended wireless device. During the permissive dialing period, affected switches operate in a mode in which routing tables such as global title translation (GTT) tables are updated to support both the old and the new NPA. If a call is directed to a MDN that includes a preexisting NPA that is listed in tables maintained at the home switch as having been split, then the switch submits the MDN dialed as the MSISDN in a query to the home HLR to obtain routing information. The HLR maps the MSISDN submitted by the switch to the IMSI associated with the wireless device and accesses the corresponding subscriber profile, which identifies the VLR at which the mobile device is registered. However, if an incoming call is directed to a MDN including the new NPA, then the switch submits a modified version of the MDN dialed as the MSISDN. The modified version includes the old NPA. In other words, during permissive dialing, the HLR has not been updated to recognize the new NPA, so the home switch always submits the pre-split version of the MSISDN to the HLR.
In either scenario, as long as the home HLR has not been updated, there is no mismatch. However, as soon as the HLR is updated, it no longer recognizes the MDN with the old NPA, because GSM HLRs lack the ability to maintain dual records for a single wireless device. Thus, if the HLR update is performed before expiration of the permissive dialing period or before the switch leaves PD mode, any calls placed using the old NPA will experience an NPA mismatch, which may cause the call to fail. Similarly, if the HLR update is not performed after the switch is no longer able to support both NPAs, the HLR will not be able to match the MSISDN with the new NPA with an IMSI and the call fails, or the home switch has to mediate the NPA mismatch by changing the MSISDN back to the old NPA and then querying the home HLR again. This raises the difficult prospect of providing the required period of permissive dialing, while coordinating updates to the HLR, affiliated network elements, switches, and wireless devices via the central provisioning system at the end of permissive dialing to avoid NPA mismatches.
Such coordinated updates of the HLR, switches, affiliated network elements, and devices associated with ported and/or pooled MDNs affected by NPA splits involve labor and resource intensive processes, including updating the HLR service subscription records to support only the new NPAs. These processes would be ideally performed in a wholesale transaction, but the central provisioning system more realistically typically performs the transaction in batches or phases according to protocols developed by IT (Information Technology) professionals employed by the carrier, which in view of the time constraint posed by the expiration of the permissive dialing period, is still a momentous effort. The typical HLR contains several million subscriber records, so bulk updates with even low error rates can create numerous customer service issues. In general, updates can only be performed in a predefined maintenance window during non-busy hours, and thus, the work must be distributed over several days. In addition, the over-the-air provisioning of wireless devices is often limited by the batch processing capability of the network, which may allow, for example, only 4000 OTA updates per night.
In the last few years, it has become even more cumbersome during these permissive dialing periods for the wireless network to determine whether a particular MDN is actually affected by an NPA split. At least two developments come into play—wireless local number portability (WNLP) and number pooling, both of which complicate the process of routing calls by analyzing the MDN.
Prior to the advent of number pooling, each carrier was assigned one or more blocks of ten thousand (10K) MDNs and thus, each carrier owned entire central office codes (NXXs). Any MDN could be easily interpreted to identify the subscriber's home HLR, and to determine whether the serving carrier had implemented a NPA split. Number pooling decreases the number of MDNs in each assigned block to one thousand (1K), frequently resulting in more than one carrier sharing a central office code. This frustrates attempts to easily map a given NXX to its home network. WLNP further obscures the relationship between the central office code and the home network, because an individual MDN that was previously served by a first carrier may have been ported to another carrier, and thus, may no longer be physically associated with the central office identified by the NXX.
Rather, when a call is placed, a gateway exchange switch determines whether the MDN dialed is in a pooled market and whether it has been ported. In direct or indirect implementations, the respective gateway exchange of the originating network or of the network that corresponds to the owner of the number block consults a remote database, such as a Number Portability database (NPDB), to determine which carrier serves the block of 1000 numbers that encompass the MDN. The NPDB responds with the Local Routing Number (LRN) that corresponds to the block or, if the MDN has been ported, the LRN indicates the carrier that serves the individual MDN. As defined in the GSM specification for supporting Number Portability, an Initial Address Message (IAM) is populated with the MDN (as a MSISDN) in the GAP (Generic Address Parameter) and with the LRN retrieved from the NPDB populated in the CdPN (Called Party Number). It is this LRN that identifies the home network, rather than the MDN as described above with respect to earlier systems.
In either case, the IAM is sent to the home switch (e.g., an MSC or GMSC) associated with the MDN, as identified by the LRN. When the call arrives at the home network, the NPDB may be consulted again. In response to receiving the IAM, the home GMSC requests routing information from the HLR, which returns the Mobile Station Routing Number (MSRN) that identifies the switch in the visited network to which the home GMSC is to route the call. The home GMSC forwards the MSISDN to the visited switch, which sets up the call to the called party. If the GMSC determines that the NPA has split or changed, it defaults to the old MSISDN—including the old NPA—before querying the HLR.
As described above, if the update of the HLR is not synchronized with the update of the affected switch by the end of the permissive dialing period, errors are received and the switch must mediate. For instance, if the NPA has split but the HLR has not been updated, the HLR will not recognize the new MSISDN if it is submitted and will be unable to return an MSRN to the recipient switch. If the old MSISDN is dialed, the HLR will request routing information from the visited switch using the old MSISDN, which will be unable to locate the called party that should have been identified by the new MSISDN.
Thus, current methodologies for mediating a NPA mismatch are limited by the inability of the GSM HLR to maintain dual records, and by the frequently excessive consumption of bandwidth as the network components repeatedly interact to mediate the mismatch.
It is readily apparent that what is needed are systems and methods for managing NPA splits that reduce the occurrence of errors as well as the bandwidth consumed in mediating the errors that do occur. Moreover, it is desirable for the systems and methods to be operational prior to or during the process of updating the HLR and affiliated network elements.